Requirements for cable trays buried in the ground

Buried cable trays must be made of corrosion-resistant materials, properly grounded, mechanically protected, and installed according to NEC and manufacturer guidelines to ensure safety and reliability.

Material Selection

For underground installations, metallic trays should be corrosion-resistant, such as stainless steel or aluminum with protective coatings, to withstand soil moisture and chemical exposure. Non-metallic trays (e.g., fiberglass-reinforced plastic) are also suitable for buried applications due to their inherent corrosion resistance . Avoid bare copper conductors in aluminum trays to prevent electrolytic corrosion; insulated conductors with proper bonding are recommended .

Grounding and Bonding

All metallic cable trays must be grounded according to NEC Article 250.96, even if the tray is not used as an equipment grounding conductor (EGC), . If the tray is used as an EGC, it must meet minimum cross-sectional area requirements based on the highest-rated protective device in the circuit (NEC Table 392.60(A)), . Bonding jumpers should be installed at tray splices or where mechanical continuity is insufficient to maintain a low-impedance path for fault currents .

Mechanical Protection

Buried trays must be mechanically protected from soil pressure, rocks, and potential excavation damage. This can include concrete encasement, protective covers, or burial at a sufficient depth as specified by local codes. Solid or ventilated covers may be used depending on heat dissipation requirements and soil conditions .

Installation Considerations

• Cable Fill: Maintain proper fill limits to prevent overheating; typically, 40–50% of tray cross-sectional area .
• Separation: Maintain separation between power and control/data cables to reduce electromagnetic interference (EMI), .
• Access and Expansion: Even underground, plan for future maintenance and expansion by providing accessible entry points or pull boxes.
• Fire and Moisture Protection: Use sealed covers or conduits where water ingress is likely, and ensure compliance with firestop requirements if the tray passes through fire-rated structures .

Summary

To safely install cable trays underground:

1. Use corrosion-resistant materials suitable for soil conditions.
2. Ensure proper grounding and bonding, with trays meeting NEC EGC requirements if used as a conductor.
3. Provide mechanical protection against soil and external forces.
4. Maintain correct cable fill, separation, and access for maintenance.
5. Follow NEC and manufacturer guidelines for installation, grounding, and environmental protection . These practices ensure electrical safety, system reliability, and compliance with code requirements for buried cable tray installations.